Hydrodynamische Instabilitäten und Strukturbildung bei der Entnetzung

在什么情况下以及在何种形态下，给定材料表面的物质是化学稳定的？这个问题定义了我们项目的研究领域。我们将研究薄（几纳米到几百纳米）的液体薄膜，这些薄膜是通过一些特殊的实验技术在固体基底上制备的。举一个工业上的例子，通过旋涂制备的CD-ROM盘的塑料抗蚀剂必须完全润湿整个盘，以安全地保护存储的信息。在实践中，大量的努力被投入到实现这样的热稳定表面中，例如粗糙化表面和/或施加粘合剂涂料。从科学的角度来看，特别是非平衡状态是具有挑战性的：液膜达到平衡状态的方式取决于许多，大部分是未知的参数。薄膜通过自发的破胶过程从表面上剥落，并形成新的结构（孔、槽等），它们的时间和空间发展以及它们的形态是我们感兴趣的中心。2平坦流体膜的对称性的破坏可以通过成核或通过流体动力学不稳定性进行。最后状态的形态是支配破碎的机制的特征。该项目的目的是通过比较不同材料类别的不同系统，找出其中一种机制优于另一种机制的条件。在薄金属和薄晶体薄膜的情况下，可以观察到流体动力学不稳定性引起的去湿。第一个结果表明，液晶薄膜表现出复杂的各种去湿图案，其中大部分还未知的起源。对于某些情况，我们可以同时了解它们的形成和发展。对于由于成核作用而引起的聚合物薄膜脱湿，我们的研究集中在寻找成核和研究脱湿过程中非牛顿流体的流动动力学。在这里，我们从优先计划中的两个小组得到了强有力的理论支持。

Under what circumstances and in which morphology is a substance at the surface of a given material thermodynamically stable? This question defines the field of research of our project. We will study thin (some nm to some hundreds of nm) liquid films which have been prepared by some special experimental techniques on top of solid substrates. To name an example out of industry, the plastic resist of a CD-ROM disk, prepared by spincoating, must wet the whole disk completely in order to protect safely the stored information. In practice, a lot of effort is put into the achievement of such thermodynamically stable surfaces, for instance roughening the surface and/or applying an adhesive paint. From the scientific point of view, especially the non-equilibrium state is challenging: The way the liquid film reaches its equilibrium state depends on many, mostly yet unknown parameters. The film beads off the surface by a spontaneous symmetry-breaking process and the emerging structures (holes, grooves, etc.), their temporal and spatial development as well as their morphologies lie in the center of our interest.That breaking of the symmetry of the flat, fluid film can proceed via nucleation or via hydrodynamical instabilities. The morphology of the final state is characteristic for the mechanism dominating the breakup. The aim of the project is to find out conditions for the dominance of one of the mechanisms over the other by comparing different systems of variable material classes.Dewetting by hydrodynamical instabilities could be observed in the case of thin metal and thin crystal films. First results demonstrate that liquid crystal films exhibit a complex variety of dewetting patterns, most of them yet of unknown origin. For some cases, we can meanwhile understand their formation and development. For the polymer films dewetting because of nucleation, our studies concentrate on the search for the nuclei and on the investigation of the dynamics of the flow of the nonnewtonian fluid during dewetting. Here, we get strong theoretical support from two groups within the priority program.